1. Field of the Invention
This invention relates generally to a medical device. More specifically, the invention relates to a catheter for insertion over a guidewire through a patient's vasculature, the catheter having a low friction guidewire lumen.
2. Background of the Invention
Cardiovascular disease, including atherosclerosis, is the leading cause of death in the U.S. The medical community has developed a number of methods and devices for treating coronary heart disease, some of which are specifically designed to treat the complications resulting from atherosclerosis and other forms of coronary arterial narrowing.
One method for treating atherosclerosis and other forms of coronary narrowing is percutaneous transluminal coronary angioplasty, commonly referred to as “angioplasty” or “PTCA”. The objective in angioplasty is to enlarge the lumen of the affected coronary artery by radial hydraulic expansion. The procedure is accomplished by inflating a balloon of a balloon catheter within the narrowed lumen of the coronary artery. Radial expansion of the coronary artery occurs in several different dimensions, and is related to the nature of the plaque. Soft, fatty plaque deposits are flattened by the balloon, while hardened deposits are cracked and split to enlarge the lumen. The wall of the artery itself is also stretched when the balloon is inflated.
Conventional angioplasty guidewires typically include a proximal shaft, an intermediate section and a flexible distal tip. The proximal shaft comprises a solid wire or a solid wall tube. The shaft primarily functions to guide and support a catheter, and to smoothly transmit rotation from the proximal end to an intermediate section.
The intermediate section extends axially from the proximal shaft and generally comprises a tapered core wire surrounded by a coiled spring and typically has more flexibility than the proximal shaft. Like the proximal shaft, the intermediate section must assist in guiding the catheter and smoothly transmitting rotation. However, some degree of flexibility in the intermediate section is desirable to conform the catheter to the curvature of the aortic arch and the coronary arteries.
Extending from the intermediate section at a distal joint is the flexible distal tip that accepts a pre-formed curved shape resembling a “J”. The curved tip tends to steer the guidewire in the direction of the hook.
All balloon catheters must have an inflation lumen through which a fluid can be forced to pressurize the balloon. As such, catheter typically have at least two lumens (viz., a guidewire lumen and an inflation lumen). Catheters having more than one lumen are commonly referred to as “dual-lumen” or “multi-lumen” catheters.
Multi-lumen catheters have cross-sections in a variety of shapes. FIGS. 1 and 2 are examples of prior art, dual-lumen catheter cross-sections. FIG. 1 is a cross-section of a coaxial catheter 100. Coaxial catheter 100 includes an inner tube 102 and an outer tube 104. Inner tube 102 defines an inner lumen or guidewire lumen 108 adapted to receive a guidewire 106. An annular inflation lumen 110 is defined between inner tube 102 and outer tube 104, and is in fluid communication with an interior of a dilatation balloon (not shown).
In use, a guidewire is introduced into a coronary artery and is steered by manipulation of its proximal end, while being observed under a fluoroscope, until the guidewire passes through a stenosis site in the artery. Once the guidewire is in place at the treatment site, a balloon dilatation catheter is advanced over the guidewire, being thus guided directly to the stenosis site so as to place the balloon within the stenosis. Once so placed, the balloon is inflated under substantial pressure to dilate the stenosis.
The anatomy of coronary arteries varies widely from patient to patient. Often a patient's coronary arteries are irregularly shaped and highly tortuous. The tortuous configuration of the arteries may present difficulties to the physician in proper placement of the guidewire, and advancement of the catheter to the site of the stenosis. A highly tortuous coronary anatomy typically will present considerable resistance to advancement of the catheter over the guidewire.
With some types of catheter construction, the increased resistance may cause a tendency for portions of the catheter to collapse or buckle axially. For example, in a catheter having a shaft formed from inner and outer coaxial tubes, such as is shown in FIG. 1, and a balloon mounted to the distal ends of the tubes, there may be a tendency for the tubes to “telescope” when presented with an increase in resistance. The telescoping of the tubes tends to draw the ends of the balloon together slightly, but sufficiently to permit the balloon to become bunched-up as it is forced through the stenosis. This bunching-up of the balloon makes it more difficult for the balloon to access the stenosis site.
Additionally, it is sometimes necessary for the physician to place a torque load on the guidewire in an effort to overcome resistance encountered in a vessel. A torque load applied to a coaxial catheter can cause the outer tube to twist, while the inner tube remains stationary, causing a rotation of the tubes relative to one another.
FIG. 2 shows a cross-sectional view of a non-coaxial, dual-lumen catheter 200. An inflation lumen 202 is in fluid communication with an interior of a dilatation balloon (not shown). A guidewire lumen 204 is defined at least in part by inner tubular member 206 which extends the entire length of the catheter body. A guidewire 208 is shown within guidewire lumen 204. As explained above, a catheter is slid over the guidewire through a tortuous blood vessel. Because guidewire lumen 204 is not coaxial with inflation lumen 202, the guidewire is not centrally located in catheter 200. Thus, when a torque is applied to the catheter to traverse the twists and turns of a body lumen, the catheter does not rotate smoothly. Instead the catheter has a tendency to “flip” in response to an applied torque because the center of gravity of the catheter is not centrally located within the catheter shaft.
When inserting a catheter over a guidewire, friction between the two pieces occurs whenever the guidewire contacts the wall of the catheters guidewire lumen. If both the guidewire and the guidewire lumen of the catheter have circular cross-sections with substantially equal diameters, as shown in FIGS. 1 and 2, tracking of the catheter over the guidewire is diminished due to friction between the guidewire and the catheter guidewire lumen. Further, in navigating tortuous areas of a vessel where the catheter body is often “flexed,” such a guidewire lumen will deform and thereby contact a substantial portion of the outer surface of the guidewire.
Further, in some convention catheters, such as a coaxial over-the-wire catheter, a physician must push the catheter from a coaxial position primarily, such that the force is primarily applied to an outer shaft. Thus the outer shaft may become misaligned or “bunch” with respect to an inner shaft.
In a typical procedure, a physician will first insert and advance a guidewire to the stenosis site. An initial dilatation catheter having a fairly small diameter balloon is then passed over the guidewire to the site and the balloon is inflated to partially dilate the vessel. The balloon is then deflated and the catheter withdrawn. Balloon catheters having progressively larger balloons are then advanced to the stenosis along the guidewire, inflated, deflated, and then withdrawn in succession to sufficiently enlarge the lumen of the artery.
In order to accomplish the multiple dilatations, the original catheter must be removed and a second balloon catheter tracked to the lesion. When catheter exchange is desired, it is advantageous to leave the guidewire in place while the first catheter is removed in order to insert the second catheter without having to reestablish the path by inserting a new guidewire. To remove a balloon catheter while leaving the guidewire in place, there must be a portion of the guidewire extending out of the balloon catheter at the proximal end so that the guidewire can be held in place while the balloon catheter is removed.
Two types of catheters commonly used in angioplasty procedures are referred to as over-the-wire (OTW) catheters and rapid exchange (RX) catheters. A third type of catheter with preferred features of both OTW and RX catheters, that is sold under the trademarks MULTI-EXCHANGE, ZIPPER MX, ZIPPER, and/or MX is discussed below. An OTW catheter's guidewire shaft runs the entire length of the catheter and is attached to, or enveloped within, an inflation shaft. FIGS. 1 and 2 are typical of OTW catheters. Thus, the entire length of an OTW catheter is tracked over a guidewire during a PTCA procedure. A RX catheter, on the other hand, has a guidewire shaft that extends within only the distal most portion of the catheter. Thus, during a PTCA procedure only the distal most portion of a rapid exchange catheter is tracked over a guidewire.
If a catheter exchange is required while using a standard OTW catheter, the user must add an extension onto the proximal end of the guidewire to maintain control of the guidewire, slide the catheter off of the extended guidewire, slide the new catheter onto the guidewire and track back into position. Multiple operators are required to hold the extended guidewire in place while the original catheter is changed out.
A RX catheter avoids the need for multiple operators when changing out the catheter and therefore is often referred to as a “single operator” catheter. With a rapid exchange catheter, the guidewire is outside the shaft of the catheter for all but the distal most portion of the catheter. The guidewire can be held in place without an extension when the catheter is removed from the body. Once the original catheter is removed, a subsequent catheter may be threaded onto the in place guidewire and tracked to the lesion. However, one problem associated with RX catheters is that the exposed portion of the guidewire may become tangled with the catheter shaft during use.
In addition, there are instances when the guidewire and not the catheter must be replaced. For example, the guidewire may become damaged during the procedure or it may be discovered during the procedure that a different shape, length, or size of guidewire is needed. An OTW catheter, with the guidewire lumen extending the entire length of the catheter, allows for simple guidewire exchange. With a RX catheter, the guidewire lumen does not extend the entire length of the catheter. Therefore, the guidewire, and most of the catheter, must be removed from the body in order to exchange guidewires. Essentially the procedure must then start anew because both the guidewire and the catheter must be retracked to the treatment site.
A balloon catheter capable of both fast and simple guidewire and catheter exchange is particularly advantageous. A catheter designed to address this need sold by Medtronic AVE, Inc. of Santa Rosa, Calif. under the trademarks MULTI-EXCHANGE, ZIPPER MX, ZIPPER and/or MX (hereinafter referred to as the “MX catheter”) is disclosed in U.S. Pat. No. 4,988,356 to Crittenden et al., incorporated in its entirety herein by reference. FIG. 7 shows an MX catheter cross sectional design as disclosed in copending U.S. application Ser. No. 10/116,234, filed Apr. 4, 2002, which is incorporated in its entirety herein by reference. The MX catheter 728 includes a catheter shaft 732 having a guidewire lumen 734 which is non-coaxial to and side-by-side with an inflation lumen 737, which is reinforced by an inner tubular member 733. A cut 730 extends longitudinally along catheter shaft 732 and radially from an interior surface 735 of guidewire lumen 734 to an outer surface 736 of catheter shaft 732. A guide member (not shown) through which catheter shaft 732 is slidably coupled cooperates with cut 730 such that a guidewire 738 may extend transversely into or out of the guidewire lumen 734 at any location along the cut 730. By moving catheter shaft 732 with respect to the guide member, the effective OTW length of the MX catheter is adjustable.